It is well known that coordination anionic polymerization using catalyst systems represented by a Ziegler-Natta catalyst allows for homopolymerization of olefins and dienes. However, it was difficult to provide efficient copolymerization of olefins and dienes using such polymerization reaction systems.
Particularly, applying a copolymer of a conjugated diene and a non-conjugated olefin to the compounded rubber results in fewer double bonds in the conjugated diene unit (the unit derived from the conjugated diene compound) in the copolymer as compared with conjugated polymers, and therefore, improved ozone resistance. In addition, one of the characteristics other than ozone resistance required when a rubber composition is applied to various applications (such as tires, conveyor belts or anti-vibration rubber) includes good crack growth resistance.
For example, JP 2000-154210 A (PTL 1) discloses a catalyst for polymerizing conjugated dienes that contains a transition metal compound of group IV of the periodic table having cyclopentadiene ring structure, and also refers to an α-olefin such as ethylene as an exemplary monomer copolymerizable with this conjugated diene. However, PTL 1 does not provide a specific description of copolymerization of a conjugated diene compound and a non-conjugated olefin. Obviously, there is no description or suggestion of improving crack growth resistance by controlling cis content and cis-1,4 bond content to be greater than 70.5%. Moreover, there is no description or suggestion of improving weather resistance by controlling the content of the non-conjugated olefin (the unit derived from the non-conjugated olefin) to be 10 mol % or more.
For example, JP 2006-249442 A (PTL 2) discloses a catalyst for polymerizing olefins that consists of a transition metal compound such as a titanium compound and a promoter, and also discloses a copolymer of an α-olefin and a conjugated diene compound. However, specific manufacture and use were ensured only if the non-conjugated olefin, α-olefin, is contained in an amount within a range of 66.7 mol % to 99.1 mol %. That is, PTL 2 does not provide any specific description or suggestion of the conjugated diene compound/non-conjugated olefin copolymer containing the non-conjugated olefin (the unit derived from the non-conjugated olefin) in an amount of 0 mol % to 50 mol %, or of improving crack growth resistance by controlling the cis content and cis-1,4 bond content to be greater than 70.5%. Moreover, PTL 2 does not provide any description or suggestion of improving weather resistance by controlling the content of the non-conjugated olefin (the unit derived from the non-conjugated olefin) to be 10 mol % or more.
In addition, JP 2006-503141 A (PTL 3) discloses a copolymer of ethylene and butadiene resulting from synthesizing ethylene and butadiene as starting materials using a special organic metal complex as a catalytic component. However, the copolymer of PTL 3 has a structure different from that of the copolymer of the present invention in that butadiene, which is a monomer, is inserted in the copolymer in the form of trans-1,2-cyclohexane. In addition, specific manufacture and use were ensured only if the non-conjugated olefin, ethylene, is contained in an amount within a range of 69.6 mol % to 89.0 mol %. In this case, the ethylene content was determined by 100 mol % minus the molar content of those units derived from butadiene with a known molar content. That is, PTL 3 does not also provide any specific description or suggestion of the conjugated diene compound/non-conjugated olefin copolymer containing the non-conjugated olefin (the unit derived from the non-conjugated olefin) in an amount of 0 mol % to 50 mol %, or of improving crack growth resistance by controlling the cis content and cis-1,4 bond content to be greater than 70.5%. Moreover, PTL 3 does not provide any description or suggestion of improving weather resistance by controlling the content of the non-conjugated olefin (the unit derived from the non-conjugated olefin) to be 10 mol % or more.
In addition, JP 2000-086857 A (PTL 4) discloses a butadiene polymer having cis content of 92% and ethylene content of 3% or 9%. However, PTL 4 does not provide any description or suggestion of improving weather resistance by controlling the content of the non-conjugated olefin (the unit derived from the non-conjugated olefin) to be 10 mol % or more.